mm/memory: convert print_bad_pte() to print_bad_page_map()

print_bad_pte() looks like something that should actually be a WARN or
similar, but historically it apparently has proven to be useful to detect
corruption of page tables even on production systems -- report the issue
and keep the system running to make it easier to actually detect what is
going wrong (e.g., multiple such messages might shed a light).

As we want to unify vm_normal_page_*() handling for PTE/PMD/PUD, we'll
have to take care of print_bad_pte() as well.

Let's prepare for using print_bad_pte() also for non-PTEs by adjusting the
implementation and renaming the function to print_bad_page_map().  Provide
print_bad_pte() as a simple wrapper.

Document the implicit locking requirements for the page table re-walk.

To make the function a bit more readable, factor out the ratelimit check
into is_bad_page_map_ratelimited() and place the printing of page table
content into __print_bad_page_map_pgtable().  We'll now dump information
from each level in a single line, and just stop the table walk once we hit
something that is not a present page table.

The report will now look something like (dumping pgd to pmd values):

[   77.943408] BUG: Bad page map in process XXX  pte:80000001233f5867
[   77.944077] addr:00007fd84bb1c000 vm_flags:08100071 anon_vma: ...
[   77.945186] pgd:10a89f067 p4d:10a89f067 pud:10e5a2067 pmd:105327067

Not using pgdp_get(), because that does not work properly on some arm
configs where pgd_t is an array.  Note that we are dumping all levels even
when levels are folded for simplicity.

[david@redhat.com: drop warning]
  Link: https://lkml.kernel.org/r/923b279c-de33-44dd-a923-2959afad8626@redhat.com
Link: https://lkml.kernel.org/r/20250811112631.759341-9-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Juegren Gross <jgross@suse.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 4f88e460eb9c..94249e671a7e 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1983,6 +1983,24 @@ enum pgtable_level {
 	PGTABLE_LEVEL_PGD,
 };
 
+static inline const char *pgtable_level_to_str(enum pgtable_level level)
+{
+	switch (level) {
+	case PGTABLE_LEVEL_PTE:
+		return "pte";
+	case PGTABLE_LEVEL_PMD:
+		return "pmd";
+	case PGTABLE_LEVEL_PUD:
+		return "pud";
+	case PGTABLE_LEVEL_P4D:
+		return "p4d";
+	case PGTABLE_LEVEL_PGD:
+		return "pgd";
+	default:
+		return "unknown";
+	}
+}
+
 #endif /* !__ASSEMBLY__ */
 
 #if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT)